Traditionally wind turbine generators comprise a rotor and a stator. The wind turbine blades are connected to the rotor in the generator, e.g. through a gear. When the blades rotate, the rotor is rotated and high current electricity is produced.
In order to be able to control the rotor current and the generator output, the generator is often equipped with a slip ring unit. The slip rings are connected to their respective rotor coils by a number of cables, often made by copper. Traditionally, the cables are lead in a hollow driving shaft. To keep the cables in place, an isolating material fills the hollow shaft.
In general, heating of the cables due to electrical resistance may cause problems or it may define an upper limit of the performance of the turbine. When isolating the cables in order to keep them in place, the generated heat is practically unable to be released to the surrounding space. This often results in overheating and spoiling of the strands in the cables, and due to vibration, the strands may break, thus leading to damage of the copper cables.